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Animal Health & Disease > Fish health > Flashcards

Fish health Flashcards

1
Q

Why do farmed fish get sick

A 
Increased stocking densities (lower profit margins) 
Infected carriers (Largely brood stock) 
Infected facilities 
Poor nutrition (we are way behind) 
Substandard water quality

Biggest problem: Greater susceptibility via weakening of resistance under intensive culture conditions

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2
Q

Fish innate immunity - 2 lines of defence

A

First line of defence is external:
- Skin, scales and mucous membranes which produce secretions

Second line of defence is internal:
- Triggered by chemical signals, employs antimicrobial proteins and phagocytic cells and the inflammatory response

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3
Q

Fish immunity - Mucous

A

Skin, gills and gut are covered in mucous

Continual trapping of micro-organisms and sloughing. Inhibits colonisation of opportunistic pathogens

Mucous is a glycoprotein layer containing:

  • Immunoglobulins: antibodies
  • Lysozyme: can kill bacteria
  • Complement: mediates inflammatory response

Major player in non-specific defence system

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4
Q

Fish immunity - Skin

A 
A protective barrier 
Covered in mucus 
Specific immunoglobulins: 
- Lysozyme 
- Rapid healing

Fish skin is relatively simple in structure
Epidermis is relatively thin
Unicellular mucous glands are abundant in the epidermis

Dermis is composed of dense fibrous connective tissue
Attached to the underlying muscles by a layer of loose connective tissue
Scales of fish are located within the dermis

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5
Q

Fish Immunity - Gills

A

Covered in mucous - rapid repair

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6
Q

Fish immunity - Lymph

A

4 times the volume of blood
Important for the movement of the immune cells, chemicals and enzymes around the body
No secondary lymph nodes in fish

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7
Q

Fish immunity - Kidney

A

Major Lymphoid tissue

Most important for immunity and haematopoiesis

Early immune response handled by entire kidney

Head kidney (anterior) is important for making white and red blood cells

Head kidney also serves as a secondary lymphoid organ

Blood flows through the kidney and antigens are trapped or exposed to macrophages and endothelial cells and can capture ~70% of blood borne bacteria

Head kidney is a major producer of antibody (memory)

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8
Q

Fish immunity - Spleen

A

One of the major lymphoid tissues - secondary to kidney

Made of red and white pulp

Red pulp contains macrophages and lymphocytes

White pulp is important in plasma filtration and capturing blood borne substances

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9
Q

Fish Immunity - Liver

A

Involved in production of complement cascade - not very clear

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10
Q

Fish Immunity - Thymus

A

Production of T lymphocytes

Not always seen across different fish species

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11
Q

Fish - Non specific humoral factors

A

Soluble substances secreted in mucous, lymph and blood

Protective function by inhibiting growth of microorganisms

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12
Q

Fish immunity - Complement

A

o A lytic compound
A cascade of >20 serum proteins and glycoproteins that act as enzymes

Activated by antibodies or bacterial antigens - Lysis of pathogen cell walls

Can work at low temperatures 0-4 degrees Celsius in fish

Leads to direct killing or opsonisation and phagocytosis

Works on Gram negative bacteria

Key participant in the inflammatory process

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13
Q

Fish Immunity - Lysozymes

A

More active in fish than other higher vertebrates

Targets bacterial cell wall peptidoglycans resulting in lysis

Works best against Gram +ve bacteria (peptidoglycan is more accessible to enzyme)

Also works against Gram -ve bacteria in fish (Gram negative bacteria have a lipopolysaccharide and protein layer that surrounds the peptidoglygan layer of the cell wall)
- When the outer cell wall of Gram-negative bacteria is disrupted due to the action of complement and other enzymes expos-ing the inner peptidoglycan layer of bacteria, then lysozyme becomes effective

Can activate the complement pathway and phagocytosis

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14
Q

Fish Immunity - Cytokines

A

Cytokines are intracellular signalling molecules released from leucocytes to coordinate immune response

Interferon: Antimicrobial protein in serum - anti-viral activity, inhibits viral replication and is not virus specific

Tumour necrosis factor: Stimulated by bacterial lipopolysaccharide, results in an increase of phagocytosis, antimicrobial

Interleukins: Activate other cytokines leading to inflammation; IL-6 is also antibacterial

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15
Q

Fish Immunity - Transferrin

A

Growth inhibitor
Binds iron
Iron is essential for bacterial survival
Pathogenic bacteria may produce chelating agents to overcome this defence

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16
Q

Fish Immunity - Lectins

A

Proteins able to bind certain sugars
Activates the lectin pathway of complement
Increased opsonisation and phagocytosis

17
Q

Fish Immunity - C-reactive proteins

A

Pattern recognition proteins that are important components of the acute phase of infection/injury

Higher levels in fish

Binds to phosphoryl choline on the surface of the bacterial cell walls

Activates the complement pathway

18
Q

Fish Immunity - Natural Antibodies

A

Produced with out any apparent specific antigen stimulation

High production in fish

Low specificity-binds to bacterial, parasitic and viral proteins

Low affinity but high avidity

Activates phagocytosis and the complement pathway

Present in the: mucus, lymphoid tissue, plasma and other body fluids

19
Q

Fish Immunity - Non-specific immune cells:

A

Monocytes and tissue macrophages:

  • Most important cells in immune response
  • Produce cytokines
  • Primary cells involved in phagocytosis and first killing of pathogens

Neutrophils:

  • Primary cells in early stages of inflammation
  • Produce cytokines to recruit immune cells to damaged or infected area
  • Phagocytic

Natural killer cells:

  • Use receptor binding to target cells and lyse
  • Important in parasitic and viral immunity
20
Q

Fish Immunity - Inflammation

A

Basic protective response to tissue damage regardless of cause

Key feature is vasodilation and influx of leucocytes from blood to the site of inflammation

Arrival of the neutrophils and macrophage cells is the start of inflammation of infected tissue

The cells are attracted to the infection site by tissue damage and chemokines

21
Q

Fish Immunity - Specific Immune Response

A

Humoral immunity:
- Production of soluble antibody (immunoglobulin)

Cell-mediated immunity:
- Mediated by several cell types including lymphocytes and macrophages

Immunological memory:

  • Adaptive change in the lymphoid cell populations
  • Mounts secondary responses if challenged again with same pathogen
22
Q

Fish Immunity - T cells

A

o Cell mediated immune response
It is known that there are T cells
- Helper T cells?
- Cytotoxic T cells?

Unlike humans most of the phenotypes and how the T cells interact have not been extensively elucidated

23
Q

What are the main types of antibody produced by humans?

A

IgM, IgG, IgE, IgA & IgD

24
Q

What are the main types of antibody produced by fish?

A

IgM, IgT & IgD

25
Q

Fish Immunity - Antibody production

A

By B1 and B2 cells

B1 cells produce the natural antibodies of the innate immune system

B2 cells produce antigen specific antibodies (unsure if T helper cells play a role)

26
Q

Fish Immunity - IgT

A

Functionally active in parasitic infections of the gut

27
Q

Fish - Where will macrophages take the bacteria?

A

Kidney or spleen

28
Q

Fish - What cells are activated in the kidney and spleen?

A

T and B cells which (along with macrophages) will go back to the site of infection

29
Q

Major differences between immune response in mammals and fish?

A

Fish are ectothermic - Low temp slows down the acquired immune response = slower production of antibody & slower intracellular killing of micro-organisms

30
Q

Fish - Factors that can alter the immune response

A 
Drug treatments 
Photoperiod / season 
Life transitions 
Stress 
- Cortisol results in decreased leucocyte migration and antibody production
31
Q

Fish vaccines - Important things to consider

A

Cost
Antigen used
Adjuvant
Route of vaccination

32
Q

FISH - Vaccinations vs Chemotherpay & Antibiotics

A 
Vaccination: 
Prophylactic - Only 1-2 treatments 
No toxic side effects = better growth 
No accumulation of residues 
Pathogens unlikely to develop resistance 
Theoretically can control disease 
No environmental impact 
Chemo & Antibiotics: 
Curative
Most antibiotics given in feed - sick fish don't eat very well
Toxic side effects common 
Toxic chemicals retained in carcass 
Bacteria can develop resistance 
Cannot control viruses 
Chemicals can impact local environment
33
Q

Vaccines in aquaculture

A

Mostly focussed on salmon species (high value)

Delivery methods:
Oral: in feed - uneven distribution
Injection: labour intensive
Immersion: fish placed in vaccine bath - used for small fish

Best protection provided by injection but most expensive

Need vaccine to be low cost:

  • Low value animal
  • Large number of animals need to be treated
34
Q

Fish vaccines - Antigen

A

The antigen used is critical to vaccine success:
Bigger the better
More complex is better
Must be structurally stable

Proteins > Carbs > Lipids

Fish vaccines require more antigen than mammals

35
Q

Issues to consider when developing vaccines for fish

A

Age of the fish at vaccination:

  • Tolerance
  • Vaccine reactions, i.e. slowed growth, spinal deformation etc.

Vaccine may protect against other bacteria
- Non-specific antibody response may be useful

Animal Health & Disease (4 decks)

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